The Harry Potter movies famously had a British only cast edict. Was this the reason why Robin Williams was turned down to play Hagrid in the movie or was something else at play?
It was one of the reasons, yes, but not the only one.
It's true that because he was not British, he was told outright that it was a no go for him to have the part of Hagrid.
“Robin [Williams] had called [director Chris Columbus] because he really wanted to be in the movie, but it was a British-only edict, and once he said no to Robin, he wasn’t going to say yes to anybody else, that’s for sure,” said the casting director. “It couldn’t be.”
But had he come in to interview, his chances were fairly slim anyway since
[Casting manager Janet] Hirshenson said Robbie Coltrane was author J.K. Rowling’s first choice to play Hagrid, anyway.